MAX3051
+3.3V, 1Mbps, Low-Supply-Current
CAN Transceiver
10
Maxim Integrated
is switched off and the receiver is switched to a low-
current/low-speed state. If dominant bits are detected,
RXD switches to low level. The microcontroller should
react to this condition by switching the transceiver back
to normal operation.
When the MAX3051 enters standby mode, RXD goes
high for 4µs (max) regardless of the BUS state.
However, after 4µs, RXD goes low only when the BUS
is dominant, otherwise RXD remains high (when the
BUS is recessive). For proper measurement of standby-
to-receiver active time (t
SBRXDL
), the BUS should be in
dominant state (see Figure 2).
Shutdown
Drive SHDN high to enter shutdown mode. Connect SHDN
to ground or leave unconnected for normal operation.
Thermal Shutdown
If the junction temperature exceeds +160°C, the device
is switched off. The hysteresis is approximately 25°C,
disabling thermal shutdown once the temperature
drops below 135°C. In thermal shutdown, CANH and
CANL go recessive and all IC functions are disabled.
Applications Information
Reduced EMI and Reflections
In slope-control mode, the CANH and CANL outputs
are slew-rate limited, minimizing EMI and reducing
reflections caused by improperly terminated cables.
In multidrop CAN applications, it is important to main-
tain a direct point-to-point wiring scheme. A single pair
of wires should connect each element of the CAN bus,
and the two ends of the bus should be terminated with
120Ω resistors (Figure 6). A star configuration should
never be used.
Any deviation from the point-to-point wiring scheme
creates a stub. The high-speed edge of the CAN data
on a stub can create reflections back down the bus.
These reflections can cause data errors by eroding the
noise margin of the system.
Although stubs are unavoidable in a multidrop system,
care should be taken to keep these stubs as small as
possible, especially in high-speed mode. In slope-con-
trol mode, the requirements are not as rigorous, but
stub length should still be minimized.
Power Supply and Bypassing
The MAX3051 requires no special layout considerations
beyond common practices. Bypass V
CC
to GND with a
0.1µF ceramic capacitor mounted close to the IC with
short lead lengths and wide trace widths.
